Reference: "The strong believer is better and more dear to Allah than the weak believer, and in each of them there is good. Be vigilant for what is to your benefit and seek the help of Allah and do not falter. But when you are striken by some setback, do not say: 'If only I had done such and such,' rather say: 'It is the Decree of Allah and He does whatever He wills.' For verily the saying 'if (i.e. if only I had) begins the work of the Devil." Muslim 4/2052.